Radiology is the branch of medical science dealing with medical imaging for the purpose of diagnosis and treatment. The practice of radiology often involves the usage of X-ray machines or other radiation devices to perform the diagnosis or administer the treatment. Other practices of radiology employ techniques that do not involve radiation, such as magnetic resonance imaging (MRI) and ultrasound. As a medical field, radiology can refer to two sub-fields, diagnostic radiology and therapeutic radiology.
Diagnostic radiology deals with the use of various imaging modalities to aid in the diagnosis of a disease or condition in a subject. Typically, a wide beam of X-rays at a relatively low dosage is generated from a radiation source and directed towards an imaging target. An imager positioned on the opposite side of the source with respect to the imaging target receives the incident radiation and an image is generated based on the received radiation. Newer technology and advanced techniques allow for improved image collection with the application of computerized tomography (CT) to medical imaging techniques. Conventional medical imaging processes involving CT scans typically produce a series of 2-dimensional images of a target area which can be subsequently combined using computerized algorithms to generate a 3-dimensional image or model of the target area.
Therapeutic radiology or radiation oncology involves the use of radiation to treat diseases such as cancer through the directed application of radiation to targeted areas. In radiation therapy, radiation is applied (typically as a beam) to one or more regions of the targeted area at pre-specified dosages. Since the radiation can be potentially harmful, extensive treatment planning may be conducted, sometimes far in advance of the actual treatment sessions, to pinpoint the exact location(s) to apply the beam, and to limit unnecessary exposure to the radiation to other areas in the subject. The treatment planning phase may include the performance of CT scanning or other medical imaging techniques to acquire image data, that can be subsequently used to precisely calculate the proper position and orientation of the subject, location of one or more target areas within the subject, and the required dosage(s) of the radiation applied during therapy.
Since the treatment planning stage may precede the actual therapy session by a substantial period of time, further imaging may be performed immediately prior to, and/or in conjunction with the application of radiation for therapy to verify the position and orientation of the subject and target area during therapy. The images acquired during the treatment application (and/or in the positioning period immediately prior to the treatment application) are compared to stored image data acquired during the treatment planning stage. Typically, an automatic process is performed by computer-implemented software that matches the images acquired during treatment (or positioning) with the stored image data. Unfortunately, automatic matching is not always effective or accurate. On these occasions, manual matching of the acquired verification image with a reference image (generated from stored, previously acquired planning images) is required.
Manual matching is typically performed by a radiologist, technician, or other such user through a computing system to confirm the match of characteristics in a target region of a subject as displayed in a produced verification image with the same characteristics of the same subject in a previously acquired “reference” image. Typically, one or more digitally reconstructed radiographs, or “DRRs” are generated from the pre-acquired planning images and displayed to the user alongside the verification image. A user is then able to verify or reject the generated DRR as a match with the acquired verification. A confirmed match could result in a registration between the generated DRR and the acquired verification image. If rejected, additional reference images are generated from the subject's previously acquired image data for the user's review.
Due to the demands of rendering these images quickly and clearly, generation of additional DRRs from the stored planning image can be rather processing intensive and/or memory intensive. Conventional methods for generating DRRs may include a GPU accelerated method, wherein a high performing graphics processing unit (GPU) is used to speed up the calculation of DRRs. Unfortunately, this requires that the computing system being used for manual matching actually have a high powered GPU. Machines without a discrete GPU or machines without high powered GPUs may not have sufficient capability for volume rendering.
Another solution is directed to generating DRRs using attenuation field based methods. According to these practices, an attenuation field is either pre-calculated or calculated on the fly for the desired image or scene. This attenuation field is then used as a lookup table for the actual algorithm used to generate the DRR. Yet another solution involves a shear warp method that provides quick volume rendering using a shear warp factorization of the transformation between generated DRRs. However, the creation and maintenance of an attenuation field can easily require expensive pre-computation and memory consumption. Likewise, the shear warp method, can also be extremely processing-heavy and require additional memory to perform, and as such neither is particularly ideal for generating multiple DRRs efficiently.